The present invention relates to a permanently excited electrical machine, in particular a direct current motor for vehicles.
From German Patent Disclosure DE 1160080 A1, a direct current motor is known in which the stator poles are formed of rectangular permanent magnets and pole shoes mounted on the permanent magnets. The permanent magnets are secured to a pole housing by means of adhesive bonding. The working air gap between the stator and rotor is defined by the pole shoes.
In the known direct current machines, for various reasons, such as a rough operating environment of a vehicle, material stresses in the permanent magnet cannot reliably be prevented from causing cracks and discontinuities, which can cause small splinters or pieces of material to become detached from the permanent magnet. If such material splinters get into the working air gap, this can cause seizing or blocking of the rotor. This is critical, especially if the motor is used for power-assisted steering in vehicles. It has therefore been proposed that a cylindrical magnet splinter guard be provided between the magnets of the stator and the rotor, the magnet splinter guard being retained on the stator by means of two covering rings.